Motor-control system.



W.'U. LUM.

MOTOR CONTROL SYSTEM.

APPLICATION mu) JULY 24, IBM.

1,236,726. PatentedAug. 14,1917.

wnNEssEmE- mvmon fig/72nd 10m 5 I 'monm UNITED STATES PATENT OFFICE.

"WALTER O. LUM, OF WILKINSBURG, YENNSYLVANIA, ASSIGNOB TO WESTINGHOUSEELECTRIC AITD MANUFACTURING COMPANY, A. CORPORATION OF PENNSYLVANIA.

A MOTOR-CONTROL SYSTEM.

Specification of Letters l atent.

Patented Aug. 14, 1917.

Application lied July 24, 1914. Serial No. 852,777.

with rolling mills and similar machines.

My invention has for one of its objects to provide a simple andefiicient means'for controlling the speed of electric motors by varyingthe voltages of the sources of energy and by varying the excitation ofthe motor-field windin 5 Anot er objectof my invention is to provide a.simple arrangement for connecting -a plurality of generators and motorsin circult, whereby the voltage values obtaining in the circuit will notexceed that of a single generator.

at furtherobject of my invention is to provide means for automaticallycontrolling the current supplied to electric motors in accordance withconditions obtaining in the motor circuits.

. In the operation of electrical systems comprising electric motors thatare connected in a closed circuit with generators, it is highlydesirable that the acceleration and retardation of the motors becontrolled both by controlling the voltage of the generators and byvarying the strengths of the motor fields. It is desirable also, in suchsystems, to prevent an excessive rush of current in the motor circuits,both when the motor is being accelerated and when the motor operates asa generator while being brought to. rest.

I provide a simple system in which the acceleration and retardation ofelectric motors is controlled by electromagnetic switches that aremanually controlled. A series of, relay switches, which areautomatically actuated only when the change in current value-exceeds apredetermined rate,

. operates to prevent excessive rushes of current. The severalgenerators and motors are connected alternately in circuit, and themaximum voltage obtaining in the circuit is that of a single generator.

In the accompanying drawing, the single figu're is a die rammatlc viewof circuits and apparatus em odying my invention.

Two generators 1 and 2 are connected in series with two motors '3 and 4,the generators and motors being arranged alternately in the circuit. Thegenerators comprise separately excited field windings 5 and 6, and themotors comprise similarl excited field windings 7 and 8, respective y.Current is supplled to the several field windings through conductors 9and 10 which may be connected :to any suitable source of direct current.A resistor 11, which is in series with the generator field windings 5and 6, is controlled by a series of electromagnetic switches 12, 13, 14,15, 16, 17, 1s, 19, 20 and 21. A resistor 22 which is in series with theby similar switches 23, 24, 25, 26, 27 28 and 29. The dinection ofcurrent through the generator field windings is controlled by reversingswitches 30, 31, 32 and 33. The circuits of the magnet coils of theseveral switches, except switches 12, 13, and 21, are controlled by amaster controller 34.

Three relay switches 35,. 36 and 37 comprise magnetcoils 38 39 and 40,respectively, which are connected in parallel relation with a reactancedevice 41 anda resistor 42 that are incircuit with the motors andgenerstore. The relay switch 36, which is a reverse-current relay, isprovided with a coil 43 that is connected across the terminals of thegenerator 1 and which is wound to oppose the coil 39. The circuits ofthe switches 12 and 13 are controlled bythe relay switch 37 and that ofthe switch 21 is controlled by the relay switch 35 and reverse-currentrelay switch 36. i a

Normally, the relay switches 35 and 36 are thereforeg normally closed toshort circuit a' section 0 the resistor 11. It may be assumed that thegenerators 1 and 2 are driven by any suitable prime mover and that themotors 3 and 4 are stationary. To start the motors, the mastercontroller 34 is actuated sistor 42, reactance device The generatorfield windings'are excited by means of a circuit extending from thepositive conductor 9, through reversing switch 30, conductor 44,generator field windings 5 and 6, resistor 11 and reversing switch 33 tothe negative conductor 10. The motor field windings 7 and 8 are excitedby means of a circuit extending from the tive conductor 9 throu h asection 0 resister 22, switches 23 an 24, ahd motor field windings 7 and8 to the negative conductor 10.- The main circuit extends from thepositive -brush of the generator. 1, through re- 41, armature windingsof motor 3, generator 2, and motor 4 to the negative'brush of thegenerator 1.

Further actuation of the controller operates to successively close thecircuits of the magnet coils 14, 15, 16, 17, 18, 19 and 20 tosimultaneously open close. The resistor field windings 7 and graduallycut out the resistor 11- and thus increase the excitation of thegenerator field windings. The motors are accelerated in accordance withthe resultant increase in generator- -volt'age.

In the ninth position of the-controller, the

switches 23 and 24 are opened and the switch 25 is closed. The sectionof the resistor'22 that is controlled by the switches 23 and 24 is thusinserted in circuit withthe motor- 8. Further actuation of thecontroller operates to successively close switches 26,27, '28 and 29 andto the preceding switch to 22 is thus gradually in serted in circuitwith the motor field windngs 7 and 8, and the motors are, accordingly,further accelerated. In the final or running position of the controllerthe switches 12, 13, 14, 15, 16, 1-7, 18, 19'and 20 are closed and themotors operate at their normal speed. If the controller'34 isadvanccd'too rapidly to increasethe generator voltage, a sudden rush ofcurrent occurs in the main cir-.

cuit. If the change in current exceeds a predetermined amount and occursat a predetermined rate, the reactance device 41 operates to causecurrent to fiow through the shunt circuit comprising the magnet coils ofthe relay switches35,j36 and 37, The

switch 37 then opens the circuit of the magnet coils of the switches 12and 13 to thus insert a section of the resistor ,11 in circuit with thegenerator field windings 5 and 5 to decrease the generator volta e. Theoperation of the'switch 37 occurs efore the excessive current hastraversed the main circuit because the reactance device 41 increases thedifference in potential across the terminals of the shunt circuit andthus causes the relay switches in the shunt circuit to anticipate rushesof current in the main circuit. The relay switch 37 operates, in themanner of the well known fluttering relay, to intermittently insert thatsection of the resistor controlled by the switches 12 and 13 in circuitwith the generator fieldwindings to decrease the generator .volt'ageuntil the current traversing the circuit has been reduced to a normalvalue. I

When it is desired to decrease the speed of the motors or to bring themto rest, the controller 34 is actuated toward its ofi position.- Themagnet coils of the several switches will be energized in the reverseorder to first gradually cut out the resistor 22 from the circuit withthe motor field windings and to adually insert the rea'stor 11 incircuit with the generator field windings. During the retardation ofthe'motors, they operate as generators to cause current to traverse themain circuit in the reverse direction. -In case a sudden rush of currentOccurs, the reactance device 41 acts, in the manner above described, toenergize the magnet coils of the relay switches 35,36 and 37.The.coils.39 and 43' of the reverse-current relay switch36, whichnormally oppose each other, operate to close the switch 36 and thuscomplete the circuit of the switch 21. The switch 21 then closes toshort circuit .a-

large section of the resistor 11 'and thus increase the voltage of thegenerators tosuch value that the current traversing the circuit ismaterially reduced. The switch 35 operates as a fiuttering,relay'untilthe current traversing the main circuit is reduced to a normal value.

It will be noted that I provide agsimple and eflicient means: foranticipating exces- 'sive rushes of current in the main circuit andpreventing their occurrence before any damage can result. I provide,also, a simple system by means of which the motors may be acceleratedand brought to rest safely and quickly.

While I have shown and described my invention as embodying a-system ofgenerator field control, it is obvious that it is adapted equally aswell for controlling the motor fields for obtaining-like results. i

I claim as my invention: 1. In a system of motor control, thecombination with a main circuit comprising a source of current, and anelectric motor, of a reac ance device in said circuit, and a relayswitch for controlling the voltage of said source, said switch having anactuating coil in (parallel relation to said reactance device an sodesigned that said switch operates only when the coil is traversed by acurrent of predetermined value.

Q. In a system of motor control, the combination with a main circuitcomprising a source of current, and a dynamo-electric machine having afield magnet winding, of a reactance device in said circuit, and a relayswitch for controlling the excitation of said field winding, said switchhaving a magnet coil in parallel relation to said reactance device andso designed that said switch operates only when said coil is energizedabove a predetermined degree.

3. In an electrical system, the combination with a. dynamo-electricmachine, of means for controlling the field excitation thereof, saidmeans comprising relays operable when the value of the current in thecircuit of the dynamo-electric machine changes at a predetermined rateand means for selectively controlling said relays.

4:. In a system at motor control, the combination with an electricalcircuit comprising a dynamo-electric machine, ofmanually operable meansfor controlling the value of the current traversing said circuit, andmeans for automatically controlling the value of the yoltage applied tosaid circuit only when the change in value of the current traversing,said circuit exceeds a predetermined rate.

5. In a system of motor control, the combination with a dynamo-electricmachine having a field magnet winding, of means for automaticallycontrolling the excitation of said winding in accordance with the rateof change in value of the current .traversing the circuit of saiddynamo-electric machine, said means comprising a reactance device and arelay switch having an actuating coil incircuit with said device.

6. In a system of motor control, the combination with a dynamo-electricmachine having separately excited field magnet winds ings and a resistorin circuit with said ings, of means for controlling said resistor, saidmeans being actuated when the change in value of the current traversingsaid dynamo-electric machine exceeds a predetermined rate.

7. In a system of motor control, the combination with a dynamo-electricmachine having a field magnet winding, of means comprising a pair ofrelay switches for controlling theexcitation of said field winding, anda reverse-current relay switch for selectively rendering either of saidrelay of change in value of the current traversing the circuit of saiddynamo-electric machine and the rate at which said change occurs, saidmeans comprising a resistor and a relay switch for controlling saidresistor.

9. In an electrical system, the combination with a dynamoelectricmachine, of means comprising a pair of relays for respectively varyingthe degree of field excitation of said dynamo-electric machine inopposite directions and means for selectively rendering the one or theother of said relays operative. 10. In an electrical system, the combination with a dynamo-electric machine, of means comprising a pair ofrelays for respectively'varying the degree of field excitation of saiddynamo-electric machine in opposite directions and means for selectivelyrendering the one or the other of said relays operative in accordancewith the direction of the current traversing the circuit of saiddynamo-electric machine.

11. In a system of motor control, the com bination with an electricmotor, and an electric generator in circuit therewith, of means forautomatically controlling the voltage of said generator in accordancewith the rate of change in value of the current supplied to said motor,said, means comprising a reactance device in circuit with said generatorand'a relay switch having an actuating coil in circuit with said device.

12. In a system of motor control, the combination with an electricmotor, and an electric generator in circuit therewith, of means forautomatically controlling the voltage of said generator, said meanscomprising a reactance device in series circuit relation with saidgenerator and said motor, a resistor and a relay switch having anactuating coil in circuit with said device a 13. In a system of motorcontrol, the com-- said generator in accordance with the rate Intestimon y whereof, ,I have hereunto of change in value of the currenttraversing subscribed my name this 17th day of July 10 said circuit whensaid motor operates as a 1914. enerator said means comprising. a. react-Znce deviee in circuitwith said motor and WALTLR said generator, aresistor, and. a relay switch Witnesses:

having an actuating eoil in parallel relation I M. J. ARNOLD, to saidreactance devlce. e B. B Hume.

